This cannot be backported to D7, as it would potentially break hundreds of thousands of themes. ;)
However, we absolutely need to get rid of this.
There's one more incarnation of this, which is even worse: theme_field() outputs an explicit . Can't get any more ugly. ;) Let's also fix that instance right here, right now.
In general, this patch should remove the offending white-space everywhere, instead of moving it around. If necessary, the CSS should inject an appropriate margin (or padding).
This issue was filed after Nate's request in #764
This is the same as https://www.drupal.org/node/1623574 filed against and committed in D8. It also solves #991522: Vertical tabs summaries have stray spaces.
@sun https://www.drupal.org/project/drupal/issues/1623574#comment-6998204